An image capturing apparatus such as a digital camera has been used in various purposes, and there is an increased demand to enhance quality of an image output from the image capturing apparatus. Image deterioration caused by the optical characteristics of an image capturing lens employed for forming an object image is one factor which hinders the image quality enhancement of the image. Marginal light attenuation, distortion aberration, and chromatic aberration of magnification can be given as examples of the optical characteristics which causes the image deterioration although these optical characteristics may vary depending on the optical system of a lens unit. The optical system from which the optical characteristics causing the image deterioration are completely eliminated has been difficult in recent years since miniaturization of the lens unit has been required. Therefore, there is provided a technique for correcting such deterioration in image quality by performing image processing.
It is very difficult to completely extract the optical characteristics of the lens from the image. Therefore, in order to perform such correction through image processing with high accuracy, optical correction data used for the above correction, which indicates the optical characteristics of an imaging optical system, is stored in a memory in the image capturing apparatus. In particular, in a single-lens reflex digital camera, the optical correction data for a plurality of lens units (imaging optical systems) that can be attached to that single-lens reflex digital camera has to be stored. In addition, even in the same imaging optical system, the optical characteristics may vary depending on the optical parameters such as a focal distance, a shooting distance, and a diaphragm value. Therefore, the optical correction data corresponding to a plurality of optical parameters is stored in a memory of the image capturing apparatus, so that a correction value conforming to shooting condition at the time of shooting is calculated from the optical correction data.
In Japanese Patent Application Laid-Open No. 2005-286482, the distortion aberration data serving as a discrete point on an image height-distortion aberration curve which indicates a relationship between the image height (a distance from a central position of the image) and the distortion aberration is held, and a correction value is calculated from an image height-distortion aberration approximate equation generated from the distortion aberration data.
As described above, the optical characteristics may vary depending on the optical parameters such as the focal distance, the shooting distance and the diaphragm value. There is also provided a method in which correction values corresponding to the entire optical parameters that can be acquired at the shooting time are stored as the optical correction data. However, with this method, the size of the optical correction data will be remarkably large, so that a large-capacity memory is required for the image capturing apparatus and a signal processing apparatus.
Further, with the conventional technique discussed in Japanese Patent Application Laid-Open No. 2005-286482, a problem relating to the size of the optical correction data and the correction accuracy, which arises when a shooting range varies according to the focal distance, has not been solved.